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Steel pipe sections have flanges on each end to allow a watertight connection to exist between adjacent sections. Shifts in pipe position may cause these flanged connections to come apart, causing a leak in the system. Pipelines that carry fluids having a lower specific gravity than water, such as oil, can incur additional problems. The differences in the specific gravities may cause die pipeline to become buoyant, particularly large-diameter pipelines. Anchoring devices that are used with these pipelines are also subject to deterioration.

Often problems are encountered in locating buried pipelines. A good first step is always to check for any available "as-built" information. Since steel is affected by magnetic fields, a magnetometer can be used to locate the pipeline. As discussed in Section 5.2.3, the information obtained by magnetometers can be misleading. Because of the large magnetic mass of steel pipelines, magnetometers are effective for locating pipelines than for locating cables. The buried pipe and chain locator discussed in Section 2.2.8 is an excellent tool for locating buried ferrous pipelines. A probing bar can also be used to locate the pipeline. A buried pipeline may show up on die image produced by a subbottom profiler, but it requires an experienced operator to interpret the data, and pipelines less than 2 feet in diameter may be difficult to detect.

5.3.1 Pipeline Repair Safety

When working on damaged marine pipelines, there is always the potential for injury to personnel and environmental damage. The repair crew should carefully assess the situation before proceeding with repairs. Identify the contents of the pipeline and determine if any of the following hazardous materials or conditions exist:

• Toxic or poisonous to personnel

• Explosive or suffocating

• Environmentally polluting

Personnel working on pipeline repairs involving hazardous materials must have an understanding of the hazards and have adequate personal protective equipment that is in good condition. Where the material carried is flammable or explosive, the pipeline should be purged. One method used involves flushing the pipeline with water before proceeding with repairs. Use caution as water will not remove all hazardous materials.

In general, personnel should not be allowed access to a spill area until the contaminated area has been clearly defined. If the likelihood of public access exists, suitable warnings should be placed and areas cordoned off to restrict access.

For some spilled products, the possibility of an oxygen-deficient atmosphere exists. In these cases, approved respiratory-protective equipment should be available for use.

CAUTION Where toxic hazards exist that contaminate the surrounding water and are dangerous to the diver, only approved diving gear suitable for the application should be used. Consult the U.S. Navy Diving Manual.

After hazard mitigation, determine what pipeline repair techniques can or cannot be used. For example, if the pipeline carries explosive or flammable materials then electric-arc or flame cutting and welding should not be used.

The location of other local cables and pipelines should be determined including those that cross each other.

5.3.2 Leak Location

The most common result of pipeline failure is leaking of the product. Usually the leak occurs at a bolted or welded connection as a result of pipeline movement, vibration, and subsequent seal damage. Leaks may also occur as a result of corrosion, abrasion, and contact with anchors, trawl boards, and forces from storm surge, etc.

• A substantial leak can usually be located by observing the discharge of the pumped material.

• Gas injected into the fluid stream can provide a stream of bubbles, while leaking water is more difficult to detect. Isolate sections of the pipe and use pressurized air.

• Colored dies can be injected into the liquid stream to help provide a visible trail.

• Metal pipelines buried in bottom sediments may be tracked using the buried pipe and chain locator discussed in Section 2.2.8.

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